gh-95672 skip fcntl when pipesize is smaller than pagesize

Doc/library/test.rst

@@ -536,6 +536,13 @@ The :mod:`test.support` module defines the following functions:
  :func:`doctest.testmod`.
 
 
+.. function:: get_pagesize()
+
+ Get size of a page in bytes.
+
+ .. versionadded:: 3.12
+
+
 .. function:: setswitchinterval(interval)
 
  Set the :func:`sys.setswitchinterval` to the given *interval*. Defines

Lib/test/support/__init__.py

@@ -51,6 +51,8 @@
  # sys
  "is_jython", "is_android", "is_emscripten", "is_wasi",
  "check_impl_detail", "unix_shell", "setswitchinterval",
+ # os
+ "get_pagesize",
  # network
  "open_urlresource",
  # processes
@@ -1893,6 +1895,18 @@ def setswitchinterval(interval):
  return sys.setswitchinterval(interval)
 
 
+def get_pagesize():
+ """Get size of a page in bytes."""
+ try:
+ page_size = os.sysconf('SC_PAGESIZE')
+ except (ValueError, AttributeError):
+ try:
+ page_size = os.sysconf('SC_PAGE_SIZE')
+ except (ValueError, AttributeError):
+ page_size = 4096
+ return page_size
+
+
 @contextlib.contextmanager
 def disable_faulthandler():
  import faulthandler

Lib/test/test_fcntl.py

@@ -6,7 +6,7 @@
 import struct
 import sys
 import unittest
-from test.support import verbose, cpython_only
+from test.support import verbose, cpython_only, get_pagesize
 from test.support.import_helper import import_module
 from test.support.os_helper import TESTFN, unlink
 
@@ -201,7 +201,8 @@ def test_fcntl_f_pipesize(self):
  # Get the default pipesize with F_GETPIPE_SZ
  pipesize_default = fcntl.fcntl(test_pipe_w, fcntl.F_GETPIPE_SZ)
  pipesize = pipesize_default // 2 # A new value to detect change.
- if pipesize < 512: # the POSIX minimum
+ pagesize_default = get_pagesize()
+ if pipesize < pagesize_default: # the POSIX minimum
  raise unittest.SkipTest(
  'default pipesize too small to perform test.')
  fcntl.fcntl(test_pipe_w, fcntl.F_SETPIPE_SZ, pipesize)

Lib/test/test_subprocess.py

@@ -717,7 +717,8 @@ def test_pipesizes(self):
  os.close(test_pipe_r)
  os.close(test_pipe_w)
  pipesize = pipesize_default // 2
- if pipesize < 512: # the POSIX minimum
+ pagesize_default = support.get_pagesize()
+ if pipesize < pagesize_default: # the POSIX minimum
  raise unittest.SkipTest(
  'default pipesize too small to perform test.')
  p = subprocess.Popen(